Delivery of high peak power optical pulses from a pulsed laser source to an end use apparatus through optical fiber is desirable in many laser based applications. By way of example, U.S. Pat. No. 6,249,630, entitled “Apparatus and method for delivery of dispersion-compensated ultrashort optical pulses with high peak power” and U.S. Pat. No. 6,320,191, entitled “Dispersive precompensator for use in an electromagnetic radiation generation and detection system” disclose fiber based delivery of high power ultrashort pulses and THz radiation, respectively.
In contrast to the delivery of continuous wave outputs or long pulses, nonlinear interaction of a high peak power pulse in an optical fiber can cause degradation of pulse quality. Delivering high peak intensity optical pulses can be particularly difficult if such pulses are subjected to unwanted non-linear effects. Thus, conventional wisdom suggests that the nonlinear interaction of optical pulses in the fiber is to be avoided.
Optical solitons can evolve in fibers if self-phase modulation and anomalous dispersion are balanced, as described by L. F. Mollenauer, et al., Phys. Rev. Lett. 45. 1095-1098 (1980). The soliton propagates in the fiber without breaking the pulse in the time domain. The general conditions for soliton formation are known. The optical soliton is generated in optical fiber with anomalous dispersion, balanced with self-phase modulation and associated nonlinearity. The pulse energy applicable for this soliton formation satisfies:
      E    =          3      ·                        11          ⁢                                                β              2                                                            γ          ⁢                                          ⁢          Δ          ⁢                                          ⁢                      τ            2                                ,where β2 is the second order dispersion of the fiber, Δτ is the FWHM of the laser pulse, and
      γ    =                  2        ⁢        π        ⁢                                  ⁢                  n          2                            A        ⁢                                  ⁢        λ              ,where A is the mode area. (See G. P. Agrawal, Nonlinear fiber optics, 3rd Ed., Academic Press, p. 151). However, it can be shown that the available energy of soliton pulses is limited to not more than a few tens of picoJoules (pJ) in conventional optical fibers.
If a laser pulse contains higher energy, the pulse may be compressed with higher order soliton(s) which results in splitting of pulse. Conversely, if a laser pulse contains less energy or is attenuated during propagation, the soliton will eventually vanish. Pulse distortion occurs in either case.
Therefore, a need exists for short, high peak power pulses to be delivered to an end use apparatus without the undesirable effect of pulse breaking, particularly in laser processing environments where separation of a remote laser head and an end use apparatus is desirable.